With less than a week's notice, my employer (a public school district) has informed me that I can no longer continue to invest with TIAA-CREF through my 403(b)7

I think you probably had notice that the school district was going to have to choose one and only one 403(b) provider beginning with 2009. It was not their choice - they were required to do it. There were articles about it in a number of places (google "403B changes") - here's a link to one - http://chronicle.com/news/article/2765/new-rules-from-irs-me...